Novel, potent, semisynthetic antimalarial carba analogues of the first-generation 1,2,4-trioxane artemether

Ten novel, second-generation, fluorinated ether and ester analogues of the potent first-generation analogues artemether (4a) and arteether (4b) have been designed and synthesized. All of the compounds demonstrate high antimalarial potency in vitro against the chloroquine-sensitive HB3 and -resistant K1 strains of Plasmodium falciparum. The most potent derivative 8 was 15 times more potent than artemisinin (2) against the HB3 strain of P. falciparum. In vivo, versus Plasmodium berghei in the mouse, selected derivatives were generally less potent than dihydroartemisinin with ED(50) values of between 5 and 8 mg/kg. On the basis of the products obtained from the in vitro biomimetic Fe(II)-mediated decomposition of 8, the radical mediator of biological activity of this series may be different from that of the parent drug, artemisinin (2).